DE2850748A1 - METHOD AND DEVICE FOR MICROANALYSIS BY MEANS OF X-RAY RADIATION - Google Patents

Description

PATENT ADVOCATE DIP L. -ING. J. MEINKE

46OO DORTMUND 1,

WESTENHELLWEe 67

TELEPHONE CO2313 140810

TELEQRAM DOPAT Dortmund TELEX 8227328 pat d

J, MOV.

_{D / y}

FILE NO .: 4I / 3263

Applicant

AGENGE NATIONAIE DE VALORIZATION DE LA RECHERCHE A N V A R, 13, rue Made leine Mi ehe Ils, 92522 Neuilly Sur Seine / France

description

"Method and device for microanalysis using X-rays"

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The invention is directed to a method and a device for microanalysis by means of an X-ray radiation.

We already know numerous methods for analyzing a test piece, in which the specimen is scanned with the aid of a probe for electromagnetic or corpuscular radiation and where a secondary radiation is detected, a complete analysis of a material requires im general that multiple analyzes of this material are examined by different processes, for example such as ESCA, EXCEPT, X-ray emission, X-ray absorption, X-ray fluorescence or the like. Prepare several samples of the same specimen and ζ. At the moment it is still necessary in the related investigation methods to use different devices in different devices.

In addition, one also knows the disadvantages of the methods in which one has to analyze an X-ray beam: The Calculations are weak, the devices are not very handy, the sensitivity for the investigation of light ones Elements is weak (because the proportional counter used in the is generally used with the elements to be examined, a window must be used, which the weak X-rays absorbed) and the resolution according to the energy of the X-ray photons is greater than at best 5 eV.

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We also know that the classical method of spectrometry X-ray photoelectrons (ESCA) do not allow an examination by scanning, since the surface of the illuminated Test piece by the X-rays not

2
can be reduced below cm. The area that one with

2 ESCA analyzed, can sometimes be reduced to a few μπι, which allows an examination by scanning, in which one sticks the specimen to be examined directly under the anticathode (J. Cazaux, Revue de Physique Applique "e ₃ 10 (1975) p. 263 But this method can only ever be used when examining specimens on which photoelectrons are generated.

The object of the invention is to create a solution with which a method for microanalysis by means of X-rays is made possible, which better than the previously suitable method meets the requirements of practice will and that is suitable in the already existing Equipment to be used when performing the ESCA procedure and AUGER needed to be applied.

With a method of the type described above, according to which one with the help of a bundle of primary electrons small layer of material forming the anticathode is scanned to generate X-rays that is received by a small layer of converter material in which the X-rays carry a current of

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Bringing into life photoelectrons that arise from the layer and that are subjected to an intensity measurement, this becomes The object according to the invention is achieved by measuring the intensity of the photoelectrons in the converter which consists of a Materia: which offers a simple photoelectronic spectrum and consists of there is at least one strip with weak connection energy, the properties of the anti-cathodic zone, which intercepts the beam, or the properties of an absorption layer between the anticathode and the Converter material to the right of the zone on which the primary electrons hit, lies.

In order to carry out the microanalysis of an anti-cathodic layer, the bundle of photoelectrons is analyzed by means of spectrometry according to the energy and the stratification of an element in the anti-cathode is derived from the intensity of the current of the photoelectrons from the energy characteristics of this element = the resolution according to the energy can be better be _s eY than 1 _s iia.3 allowed by the action of the chemical shift, the various oxy = dationsgrade this element highlight.

Inserted verter an absorption layer of the test piece, which schematically anticathode and the Kon for measuring the local absorption is _s one can (in particular when the sample is homogeneous) capture the photoelectrons without distinction according to the energy. But you can also

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carry out the divorce in such a way that one follows the flow of the elastic photoelectrons, be it due to the characteristic Voltage of the anticathode or be it (at least in some cases) due to the fluorescence voltage that is chicked from the object, measures,

In either case, a resolution of 10 eV. When you examine organic absorption layers If you want, you will preferably use an anti-cathode made of aluminum or magnesium. In metallurgy you use the chrome a lot more. When the absorption layer consists of a light element, it is often advantageous to form the anticathode from one element, which corresponds to those in the Mendeleiev classification follows, from which the absorption layer is formed.

The invention proposes in the same way a disc, which is useful to using the procedure described above to be used between a thick layer of a material which forms the anticathode and a thin layer of a Jionvertermaterial, made of one layer of the specimen consists, which is organic (which will lead to, that one frequently the edges of the anticathode and the Converter seals airtight to a hermetically sealed To form capsule to protect the specimen), metallurgical or mineralurgical. The material, from which the anticathode is formed can function

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to the type of absorption layer or to that of the element below as proof.

The invention is explained in more detail below with reference to the drawing, for example. This shows in

Fig. 1 is a schematic diagram showing the possibility of a disc shows in which the anticathode is covered by a layer of the Specimen to be examined is formed,

Fig. 2 is a schematic diagram that used in principle Elements of the device for carrying out the method shows,

3 shows a schematic representation in section of a disk which can be used in another embodiment according to the invention can use

4 shows a curve representative of the absorption in function to energy, which has the advantage of a corresponding Wäü. an energetic selection look in borrowed should do.

In a first embodiment of the invention, the method is used to perform a microanalysis of a

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Test piece, which forms the anticathode, to carry out by identifying its characteristic X-ray radiation. For this purpose, one measures the kinetic energy E _{R of} the collected photoelectrons, which originate from a converter layer, and one derives the energy hu of the X-ray radiation \ on the kinetic energy E _R and the binding energy E _{ß of} the essential material of the anticathode through the following relation:

h μ = E _B + E _K.

By placing an analyzer on a kinetic Energy E ^ corresponding to the energy h u of the X-rays, which results from the excitation of a certain element, one can determine the distribution of the X-ray derivation of this element in the middle of the anticathode.

The anti-cathodic layer and the converter layer are connected to form a composite disk, as is shown schematically in Pig »1. The disc 10 carries a anticathode 11 _s consisting j which to analyze from a layer of the specimen, covered with a layer 12 whose thickness is weak and good determined from a converter material, the nature of which is known, consisting of an element or of a pure Substance selected depending on the element or elements that one wants to detect in the material of the layer that has the anti-

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cathode forms, according to the criteria that are described below.

The method can be carried out in a device whose construction is generally that of an AUGER microscope is equivalent to. The device is shown schematically in Fig. 2 and carries an electron tube 13, the is equipped with an optical system, which delivers a fine bundle of primary electrons 14, which the electronic Form a probe, focused on the disk 10. Using suitable optics, one can achieve a resolution in the Reach the order of magnitude of a mys.

The electron beam 14 is under the influence of a scanning device subjected, indicated schematically by two pairs 15 and 16 of lead coils, which in two mutually perpendicular standing directions are arranged »but mano can also in the same way the scanning of the disc 10 in a conventional manner, for example in the manner of the heel technique, eriö.chen.

An analyzer 17, for example in the form of a cylindrical mirror, the description of which is not necessary since it is well known, and with which a resolution of the order of 0.1 eV in the area of 100 up to 500 eV, collects the photoelectrons which originate from the converter material 12. An intensity

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measuring element 18 of the analyzer is equipped with an amplifier electronics 19 connected, the output of which a display device 20 feeds, for example, a cathode screen. This device is connected to a command circuit 21 for scanning, which the synchronicity between the scanning of the composite Disk 10 ensures from the bundle of primary electrons 14 with that of the viewing device.

The bundle of primary electrons creates in the layer 11 X-rays characteristic of the elements that guide them and that scatter in all directions. A part of this radiation penetrates the layer 11 and meets the layer 12 of converter material, where it generates photoelectrons. These photoelectrons that the Layer -12 ent weed, are captured by the analyzer 17 at a fixed angle as high as possible, the Analyzer 17 analyzes them according to the energy and for example can be suitable to correspond to a characteristic X-ray radiation of an element to be detected.

The thickness of the layer that forms the anticathode is selected as a function of the energy of the primary electrons. In practice, the maximum voltage for accelerating the electrons becomes 20 kV for the sake of convenience for reduction the space requirement of the tube and the costs are not exceeded. For the most part, one gets the tension

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to about 10 kV "limit what the device In the same Way of analyzing spectrometry according to AUGER and according to ESCA (chemical analysis by spectrography of electrons) makes suitable.

In these conditions an anticathode is generally used, which has a thickness of less than 10 μ. On the other hand, since it is desirable that the primary electrons are practically completely absorbed by the anti-cathode layer, this generally has a thickness of less than 0.5 μ.

The converter material is generally made of a pure element in order to have a good quantum yield and a simple one as possible spectrum and it is appropriate with the type of element which is to be tracked in the anticathode is. Every time you want to track down light elements, it is useful if the element which forms the converter, has the lowest possible binding energy Eg.

In particular, gold can be used, which has the advantage of increased quantum education. In this case you use a doublet, consisting of a high degree of gold, with binding energies Eg of 83 eV and 87 eV. Gold has different Pros: It is a good conductor of heat and easy to shape into a fine layer of uniform thickness; it allows, detect all elements except lithium, helium and hydrogen.

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If you have a mixture between several photoelectronic rays that are different from X-rays Energy to be stimulated, to avoid desires, and to preserve the possibility of lowering light elements Amorphous carbon or boron can be used to track down atomic number. The disadvantage of using a carbon layer as a converter consists in the impossibility of tracing the carbon itself (often in organic samples), just like the even lighter elements, especially boron, birilium or lithium.

In some cases, one can also use simple bodies to form the converter layer. In particular the use of lithium fluoride allows the discovery of very light elements, the binding energy of lithium is very weak.

The thickness of the converter layer corresponds to the thickness the ejection of photoelectrons so that one is generally made to have a very small thickness take which does not exceed 0.5 μ, which can easily be jralized by evaporation if the material is the Layer is suitable for this.

The relative resolution according to the energyÄE / E of the spectrometer to the electrons can easily reach 10. Polly one can trace the rays K 06 up to the zinc, like this

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like the rays L or M for the heavier elements with an absolute energy resolution ΔE that is up to 0.1 eV can be lowered.

In a second embodiment of the invention is placed between the anticathode, which consists of a pure element or a simple body, and the Converter layer of small and regular thickness, also made of a known material, a layer of the specimen to be researched. The intensity of the flow of photoelectrons emerging from the converter is fixed to the dependence on the absorption of X-rays the specimen emerging from the anticathode.

Depending on the type of analysis, the measurement acting on the flow of photoelectrons will be different.

In particular, you can collect all photoelectrons, whatever their energy is. That is then, for example be the case when you consider the differences in thickness want to determine a homogeneous layer of a sample.

In the same way, one can use a bound energy analyzer to find the elastic photoelectrons, which are triggered by the X-rays from the aticathode and have crossed the specimen or around the fluorescence X-ray radiation

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to track down the electrons emitted by the specimen will.

In any case, a disk is generally used, the basic structure of which is shown in FIG. 3 (in which the Elements which correspond to those from FIG. 1 have the same reference numerals and are provided with an a as an index are).

The layered disk 10 ″ carries an anti-cathodic one

Cl-

Layer 11. which is generally of an element in pure

State is formed, generally from a metal j which preferably has an increased thermal conductivity. The voltage to accelerate the primary electrons, which form the scanning beam "14_ exceeds in general

cL

common not 10 kV. One generally becomes the K-ray of the light and intermediate elements (up to zinc, whose atomic number is 30) and the L or itself the M radiation for the heavy elements. This is in same catfish for the first embodiment of the invention valid.

Every time the specimen to be examined from light Elements, such as carbon, nitrogen, and oxygen, are principally made up of biological samples Form, one tries to increase the absorption contrast to use an X-ray radiation and therefore

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An anticathode made of aluminum or magnesium is preferable, the K06 radiation of which is excited.

In contrast to this, in metallurgy or mineralurgy one may be interested in the use of the Ko ^ radiation from chromium. The thickness of the layer 11 of the anticathode will then be the same as in the exemplary embodiment according to FIG Fig. 1.

Of course, you can also divide the test piece to be checked into several samples by, for example different anticathodic by vapor deposition Applies layers in order to achieve different contrasts of the element to be determined and at the same time a Realize inversion with contrasts. In order to achieve a maximum contrast, it is advisable to use an anticathode 11. to use, which triggers an X-ray radiation χ, de-

ren wavelength is slightly below that of the absorption of the element to be examined in the sample. As shown in Fig. 4, the absorbance (on the ordinate) of a given element be very much higher if we assume an x-ray whose energy is a little in excess of that which is indicated at 22 in Fig. Ά. The test piece 24 presents itself as a layer, the thickness of which is chosen as a function of its absorption. One can assume a thickness at which the absorption

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V 285074?

e "^ ^{x is} between about 10"'and 0.9, but in practice the thickness will be between about 0.3 and 30μ.

Finally, to form the converter layer 12 _Q

take the same elements as in the case of Fig. 1. Since the analysis according to the energy of the photoelectrons if one using this, not a very high level energetic resolution is required (an absolute resolution Δ E of the order of 10 eV is sufficient if one does not see the effect investigated chemical sliding, one can almost always use a thin layer of gold, whose Thickness does not exceed 0.5 u meters).

If one considers the absorption of X-rays by a To examine a test piece of a light element such ^, it is generally appropriate to use an anticathode which consists of an element which is in the Mendeleiev classification follows the element to be tracked. For example, aluminum and magnesium in thinner To track down the layer, the anticathode can be formed from a thick layer of silicon or aluminum. That Converter material can be amorphous carbon or gold in both cases.

The layers that represent the anticathode and the converter, can form a hermetically sealed capsule, in which the specimen is safe from the vacuum effects,

- ν * ■ -

which prevail in the device is introduced. This' possibility represents a great advantage to living Investigate particles, because if they were subjected to a vacuum, they would be killed immediately by the dehydration would.

As stated above, the second embodiment of the invention can be used to determine the absorption distribution of X-rays by the specimen. In this case it is advantageous to use a collecting electrode 25 instead of an analyzer for the energy which collects all the photoelectrons leaving the converter. This is how you measure a maximum photoelectron current for a predetermined intensity of the primary photoelectron current, which allows, either to carry out a very fast measurement or a very narrow but much weaker current corresponding to it Pick up bundles of primary electrons (therefore to provide a better definition).

To take note of it, one can see that one

global quantum yield on the order of 10 " can come in the absence of the sample, with an anti-cathode made of aluminum and a converter coating made of gold. With an energy lesson according to a gap or a window of 10 eV can be achieved when using a field emission tube, a considerable flow of primary elec-

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tronen delivers, achieve a resolution on the order of 0.5μ by maintaining a storage speed of the slow bidirectional mapping. If all the electrons that are ejected by the converter are taken into account, the measurement intensity is increased considerably, which is multiplied by a factor of about 10 ⁵ , because a continuous remainder of secondary electrons and photoelectrons adds to the corresponding flow of photoelectronic beams , which are subjected to elastic collisions in the test piece and in the converter, and a resolution of about 0.5 μ can be achieved with a normal scanning speed.

As an example of the method according to the invention by absorption, one can cite the non-destructive testing of integrated circuits of microelectronics. In fact, one can measure the thickness of an insulator in conventional structures of the type of metal-oxide-semiconductor or metal-insulator-metal by using that or one of the metals as a converter. For example, in the case of a MOS structure of the Au-SiOg-Si type, the silicon can be used as an anticathode and the gold as a converter material and the gaps in the SiO ₂ layer and their defects in homogeneity can be measured. The same method can be used in the case of a MOS structure of the Al-SiOg-Si type. This latter layer, generally made up of several Mys, also forms the anticathode.

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- st- -

If one can not do more than simply examine the differences in the absorption of X-rays by the sample layer, the follows in two directions, wants to investigate, but rather to determine the distribution of a given element in this layer one will generally prefer to make an analysis according to energy.

In general, such an energetic analysis is achieved by regulating the analyzer in such a way that its energy gap in the spectrum corresponds to the elastic photoelectrons which emerge from the converter layer by the characteristic X-ray radiation emitted by the anticathode. Some naturally release the photoelectrons generated in the part of the converter layer corresponding to the amount of leakage based on the exit side. This gap is determined taking into account the fact that the kinetic energy Ε _{χ of} the photoelectrons in addition to the energy h \) of the X-rays emitted by the anticathode and the binding energy E _{ß of} the photoelectrons are given by the relationship:

^E K = ^h0 c - ^E B

In some cases it is possible to regulate the analysis in such a way that the measured current corresponds to that of the photoelectrons which is emitted by the fluorescent radiation

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that emanates from the object and the energy hυ _f. In this case the kinetic energy of the photoelectrons is given by the following relation:

= h \) _f - E _B.

One can also determine the distribution within an element, especially in a layer, by making an energy selection that _{corresponds to the value h \) f} , which characterizes this element: Such a process can be used, for example, to determine the distribution of the elements with average atomic numbers determine, for example, the chromium in a sample. It must be noted that the fluorescence radiation is of course much less intense than the anticathode radiation and that consequently the currents are very much weaker and the implementation of the process is therefore much slower.

In any case, the method can be applied in an apparatus which in like manner of other types of analyzes can serve. The method according to the invention can also be used in other known methods apply together with these, and to a certain extent to which the procedures can be substituted. ·

Of course, the exemplary embodiments described are still valid to change in many ways, without the basic idea

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to leave the invention. The procedures are not limited to use within a specific device, At the same time, devices equipped with a cylindrical mirror analyzer can be used or to which a device for collecting all the imitated photoelectrons is added, possibly equipped with a reinforcement (e.g. flat coil of a microtube).

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Claims (12)

Expectations : ( Γ.) Method for microanalysis by means of an X-ray radiation, "-"'according to which a small layer of material, which forms the anticathode, is scanned with the help of a bundle of primary electrons in order to generate an X-ray radiation that is transmitted by a small layer of converter -Material is received in which the X-rays give life to a stream of photoelectrons, which arise from the layer and which are subjected to an intensity measurement, characterized in that one of the intensity measurement of the photoelectrons generated in the converter is made of a material consists, which offers a simple photoelectronic spectrum and consists of at least one strip, with weak connection energy, which derives the properties of the anti-cathode zone (Ii), which intercepts the beam, or the properties of an absorption layer (24), which lies between the anti-cathode (Ila ) and the converter material (12a) is to the right of the zone. 2. The method according to claim 1, characterized in that the primary electrons (14) have an energy lower than 20 keV, the anticathode (11) have a thickness of approximately 0.5 to 10 My and the converter (12) has a thickness of less than 0.5 My. 3. Procedure according to. Claim 1 or 2, characterized in that that one subjects the photoelectrons to a selection according to the energy before the intensity measurement. 90 98 22/070 7
ORIGINALINSPECTEa 4. The method according to any one of the preceding claims, characterized in that the converter material (12) is carbon, Boron, gold or lithium fluoride. 5. The method according to any one of claims 1 - 4, characterized in that that the intensity of the beam is displayed with a viewing device in synchronism with the scan. 6. A method for microanalysis of a material which forms the anticathode according to claim 1, characterized in that that one analyzes the beam of photoelectrons by spectrometry for energy, preferably with a corresponding energetic resolution of less or -4
equal to 10 or a perfect resolution better than 1 eV - which enables not only the identification of the elements, but also the determination of the degree of their oxidation by the action of the chemical shift and by the fact that the stratification of an element in the anticathode of the intensity of the current of the photoelectrons according to the energy characteristics of this element. 7. The method according to any one of claims 1-5 for the microanalysis of an Abs options layer, characterized in that this layer is given a thickness which corresponds to that of its absorption of X-rays (X-rays), E ~ P , and approximately between ΙΟ "- 'and 0.9 lies. 909822/0 70 7 8. The method according to claim 7 for measuring the local absorption of X-rays in an absorption layer, characterized in that the anticathode (Ha) is formed from an element which has the consistency of that Absorbent layer (24) in the Mendeüiev classification follows and from the fact that the photoelectrons are collected without any distinction in energy. 9 · Method according to one of claims 1 - 7, characterized in that that the photoelectrons of an energetic analysis with a resolution of the order of 10 eV subject. 10. The method according to any one of claims 1-5 and 9, intended for the analysis of an absorption layer (24), consisting of a biological structure which contains carbon, nitrogen and / or oxygen, characterized in that an anticathode (Ha) made of aluminum or magnesium is used 6 - " Ho method according to claim 10, characterized in that the absorption layer is hermetically sealed between the anticathode (Ha) and the layer of converter material (12a) includes - Fig. 3-. 12. The method according to any one of claims 1-5 and 9, intended for metallurgical or mineralurgical investigation, ^: 909822/0707 characterized in that the anticathode is formed from chromium and in that an X-ray radiation is used accordingly the Koi * radiation from chrome. 13 · Microanalysis device for carrying out the method according to any one of the preceding claims, characterized in that it comprises a tube capable of scanning a disk made possible by a bundle of electrons with an energy of approximately 20 keV and means for Has measurement of the photoelectron current, which are supplied by the disk, with or without selection according to the Energy, usable at will for the analysis of the X-ray emission (emission X), the X-ray absorption (absorption X), X-ray fluorescence (fluorescence X), AUGER and ESCA. 909822/0707